A medical practitioner will typically secure the airway of a patient undergoing general anesthesia to ensure proper airway ventilation. Common methods of providing proper airway ventilation include the use of an endotracheal tube (ETT) or a laryngeal mask airway (LMA). An ETT is a plastic tube that is inserted through the mouth into a patient's trachea to ensure that the airway is not closed off and that air is able to reach the lungs. An LMA is a plastic tube having an inflatable cuff at one end to be inserted through the mouth into the hypopharynx where it sits tightly over the top of the larynx.
Several problems are posed by the use of either an ETT or an LMA in an anesthetized patient. First, a patient may unconsciously and involuntarily bite down on the tube and occlude the airflow, usually during emergence (waking up) from anesthesia. This may lead to hypoxemia, a low blood oxygen level. Such occlusion of the airflow may delay the emergence from anesthetic inhalation agents and can even lead to negative pressure pulmonary edema (NPEE). NPEE may occur when the patient struggles to inhale against a partially or completely occluded upper airway. In a vigorous adult the inspiratory muscles can generate enough negative pressure to cause fluid to extravasate from the pulmonary capillaries into the interstitial and alveolar spaces. This fluid leak may result in immediate or delayed hypoxemia. Even after an upper airway obstruction is alleviated, pulmonary edema can develop immediately or up to six hours later. Second, a patient may bite down with enough force to damage the anterior teeth in contact with the ETT or LMA, especially when veneers or bridges are in employ as dental restorations or in a patient with loose or unstable anterior teeth.
Medical practitioners typically place a “homemade” roll of gauze, or sometimes a roll of gauze wrapped in tape, between a patient's molar teeth to help prevent occlusion of the ETT or LMA when the patient involuntarily bites down. However, this may be an unsatisfactory approach because the gauze can slip out of place or alternatively be compressed down with involuntary biting thereby allowing the ETT or LMA airway to be compressed and occlusion thereof to occur.
A dental bite block may also be unsatisfactory because it is designed for use on awake patients and is designed to keep the mouth opened wide for access to posterior teeth. Furthermore, a dental bite block is typically small and completely intra-oral in application and could fall into the back of the throat during ETT or LMA removal, resulting in gagging or airway obstruction, and may also prove difficult to extract from the patient's mouth after removal of the ETT or LMA.
Bite blocks designed for endoscopy are designed to reside anteriorly between the incisors of the patient, and are unsuitable for anesthetized patients as biting forces will be applied to the incisors. The incisors are. less suited than molar teeth to withstanding the forces generated in clenching of the jaws in anesthetized patients, increasing the risk of dental injury.
A prior attempt at producing a bite block compatible with an ETT or an LMA is disclosed in U.S. Pat. No. 5,655,519 to Alfery. Alfery discloses a wedge shaped bite block having upper and lower non-incisor teeth engagement surfaces. The bite block is angled such that the non-incisor teeth engagement surfaces gradually become farther apart in a direction from the posterior portion toward the anterior portion, to thereby hold a patient's incisors apart when the bite block is positioned in the patient's mouth at one side thereof. Two pairs of spaced apart flanges extend from the bite block to limit lateral movement of the bite block in the patient's mouth. A handle is included for facilitating positioning of the bite block within the patient's mouth and for removing the bite block. Alfrey's design has a drawback in that it is complex to manufacture as it uses different materials for construction of the handle and the teeth interfacing aspect, respectively. This may render the bite block too expensive for disposable use. In addition, it is unclear as to how the handle is anchored to the teeth interfacing portion, creating concern that the two may become separated during clinical use leaving the smaller teeth-interfacing portion loose in the mouth. This would create a risk of dislodgement and loss of the bite block into the patient's pharynx and the potential for subsequent airway obstruction, and then the small nature of this portion of the bite block could be difficult to retrieve and remove. In addition, the handle may prove cumbersome and impractical in routine use in anesthetized patients, especially in patients undergoing head or neck surgery, or in those patients who require prone positioning, for example in spinal surgery. Lastly, the flanges in Alfery's device are elongated and may rest against the gingiva of the patient and, in surgeries requiring an hour or more, this could contribute to gingival compression injuries.
Another bite block is shown at www.kingsystems.com/PRODUCTS/AirwayDevices/FlexBlueBiteBlock/tab id/164/Default.aspx. This bite block may, however be unstable when placed in a patient's mouth due to its semicircular molar engaging surfaces.
A further attempt at a bite block is described in U.S. Pat. No. 4,495,945 to Liegner, which discloses a bite block for use in an endoscopy procedure. This bite block has teeth receiving channels that are in contact with all of the patient's teeth. As such, when a patient bites down, the bite force is distributed among all the patient's teeth, including weaker teeth such as the lateral incisors and canines. This may lead to damage of these teeth.
U.S. Pat. No. 5,386,821 to Poterack described a bilateral bite block for use in a patient's mouth with an ETT in place. A handle connects the two sides of the bite block, but the molar interfacing surfaces are angled in a manner that may allow displacement of the sides laterally into the cheek pouches. This might result in contact between the patient's molar and a loss of function of the bite block.